A lawsuit in progress against Linden Lab has already set an important precendent regarding "Terms of Service Agreements" and virtual worlds. The lawsuit itself regards a land dispute, and Linden Lab moved to dismiss the case or move the proceedings to private arbitration. They were denied on the basis that the Terms of Service were agreed upon in an unfair "take it or leave it" situation where the user had no bargaining power according to 3pointD.
While in another situation that might not have mattered so much, Second Life is advertised as a place where people can earn real money. As a result, it is subject to a higher set of standards and cannot arbitrarily decide what the rules are.
This will have extremely broad ramifications for virtual worlds in the future. You can view the full legal brief here.